1. Field of the Invention
The invention relates to a valve having temporary and permanent lock open mechanisms, adapted for downhole use in a subterranean well.
2. Description of the Prior Art
Valves used in subterranean wells, such as flapper-type safety valves responsive to a pressure signal, are known in the art. A typical normally closed valve may be held open by means responsive to a fluid pressure control signal from the surface. When the control pressure is reduced, the responsive means is actuated to permit the valve to close. It is often desirable for such a valve to have a releasable temporary lock open feature, whereby the valve may be locked open without the necessity for a continuous pressure signal. Some prior designs have included a temporary lock open mechanism incorporated as an integral part of the valve opening and closing mechanism. For example, the lock open mechanism has commonly been included in a moving plunger which directs the valve to open position. The placement of the lock mechanism on the plunger presents the possibility of a malfunction in which the lock mechanism would fail to release, or would stick, as an attempt was made to withdraw the plunger and close the valve.